The present embodiments relate to ultrasound imaging. In particular, ultrasound viscoelastic imaging is improved.
Several commercial ultrasound systems provide quantitative values or images of tissue stiffness, such as stiffness measured using shear wave imaging. The stiffness is estimated by assuming that the tissue is purely elastic (i.e., assuming that viscosity is negligible). Different approaches are used for measuring stiffness. These different approaches may emphasize different bands of the shear wave frequency spectrum even while assuming that the tissue is purely elastic. For example, some approaches find a peak displacement caused by the shear wave while others find a peak in a derivative of the displacements. The derivative function alters the frequency band being measured. As a result, different ultrasound systems provide different values for the stiffness or shear wave parameter even for the same tissue. Further, human tissue is viscoelastic, so shear wave dispersion is present. Different shear wave frequencies travel at different speeds. The dispersion is governed by the frequency-dependent storage modulus μ1 and loss modulus μ2.